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N/S vs. E/W PV orientation


Chris Knipe
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Hi Guys,

So I figured I'd rather start a new thread.  We all know what happened and I think I am at the point where I am going to write my Axpert off - permanent by-bass has been wired into the DB.  I was intending to upgrade the system *significantly* in any case... Thankfully now, I have decided to look at Victron and I am impressed - it's bound to be a better choice than the Axperts / Infinity / etc.

One of the big obstacles I've had in the past with my current system, was that I do not have a lot of north facing roof space.  It doesn't matter what you do or how you look at it, there simply isn't space and you can't magically invent space either.  My house's roof orientation is unfortunately South East/ North West, but I have a LOT of South East / North West space available.  Looking at Victron's BlueSolar MPPT's now, I see that they can be paralleled? 

Whilst I understand you will loose some efficiency as only half the panels will work in the morning, and the other half will work in the evening (and both should work during mid-day hours)... Would it work to connect two of these units in parallel and have one charger on the East facing panels, and another on the West facing panels?  I am confident they will get more than sufficient sunlight, I can put up more than sufficient panels.  I can easily max out a 150/70 or 150/80 on each side of my roof I reckon in terms of max PV input power... The idea here is to generate and store as much as possible, to go off grid completely.  I haven't crunched the numbers yet though so the discussion is theoretical at this stage. I am more than likely going to go a bit big and look in the 6kW to 8kW region for PV though (currently have 3kW installed on my grid-tied system).

Yes, I know it won't be as efficient. Yes, I know I will need more panels. Yes, I will more than likely need two Chargers.  Technically speaking, no reason why it wont work though, right?

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2 hours ago, Chris Knipe said:

Looking at Victron's BlueSolar MPPT's now, I see that they can be paralleled

If you have all the equipment to set up an ESS system, in other words you also have a Venus-GX control unit and the cables, then the inverter controls the solar chargers, it sets the charge voltage and they all switch from absorb to float in unison. That is really all that is meant by paralleling. Because the term is so confusing, the newer versions of the firmware refers to "networked operation" instead.

2 hours ago, Chris Knipe said:

have one charger on the East facing panels, and another on the West facing panels?

If you put them on separate MPPTs, then they don't affect each other. You can also put an east/west array onto the same controller (with the PV arrays in parallel into a single controller), but there is a slight production loss if you do this. In your case, the fact that there is "South" involved as well makes me question things. If I'm putting panels on the South East side, they'd have to be on a separate MPPT.

Panels pointing North West don't do too badly. They start producing a little later in the day, but especially in summer it does very well. North East is also not too bad, but I have a bad feeling about South East. Especially in winter.

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Thanks @plonkster

It's not a lot south east.  I'd say more east/west than anything.  Both sides get plenty of sun during the winter and summer months.  Been keeping my eyes on it for a few years now.

I'm still trying to get my head around Victron and all their offerings yes.  I'm more than likely looking at 2 x Blue Solar and 1 x Quattro given the loads I have in mind (couple of Pylons perhaps for storage).  As far as I understand, the Quattro will control the Blue Solars yes.

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1 hour ago, Chris Knipe said:

Quattro

Quattro is Italian for four (old news, yes!), and it is called that way because it has two inputs and two outputs, 4 legs. It has two inputs so that you can put a backup generator on the other one. It can use either AC input and switch between them, which is great if you need some backup until your backup generator comes on and you want it to seamlessly switch between the AC sources and battery.

If you're not going to use the second input, save the money and get an "ordinary" Multiplus. Same inverter essentially, just one less transfer switch.

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Hi Chris

My panels are facing east west, with a little bit turned more to south/east than east and fitted at a 23 degree angle.

Attached a graph of today's production and you can clearly see how early in the morning the west array is already active. Yes I have 2 separate MPPT's and it works very well.

The negative part is that during the winter months of June - August I lose more production than what I would have if it was facing North.

The ideal for me would be to have an east / west array as well as a portion of panels facing north .

I am currently installing a system at my offices and is doing exactly this, I will be able to see whether my theory is correct within the next 3 - 4 weeks.

2133145924_10-10-2018gen.thumb.jpg.1a0d6967fdfcd616f111168db9408d1e.jpg

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Perfect, thank you @Chris-R - that graph is almost EXACTLY what I expected to see.

This is exactly what I was after.  Yes generation in winter is expected to be less, however, I still feel that it can be justified (some PV, is better than NO PV at all in the case that there's no North facing space available).  You can (or I can at least given the space I have available) also compensate for the lower generation in Winter by over specing the system and putting a few more panels than what is needed on. You can also if winter is a potential problem, do more on the west side with even more panels, and hope that the afternoon sun on the west side will be sufficient to carry the load and give enough to charge the batteries.  That is all things that one can address with the proper and adequate math however.

@plonkster yep - well aware of what quattro means.  Well aware of how Victron's Quattros work as well :)  

 

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